1. Technical Field
The present invention relates to a technology that, by interrupting a normal pulse-width modulation (PWM) control and carrying out a control whereby an ON time of a switching element is repeated before and after a predetermined OFF time, suppresses an output voltage reduction when the output voltage of a DC-DC converter drops below a predetermined value due to a load current suddenly increasing, or the like.
2. Related Art
FIG. 4 is a diagram showing a configuration of a general DC-DC converter control circuit for controlling an output voltage of a heretofore known DC-DC converter. In FIG. 4, an error amplifier 10 amplifies the difference between a reference voltage Vref 11 and a feedback voltage Vd 53 acquired by a voltage division of a DC-DC converter output voltage Vout 44 in a voltage divider circuit 50 that has a voltage divider resistor Rd1 51 and a voltage divider resistor Rd2 52, and outputs an output voltage Vea 12 as an output to a PWM signal generator circuit 20. The PWM signal generator circuit 20 generates a switch drive signal Vdrv 22 in accordance with the output voltage Vea 12 of the error amplifier 10 (in this case, the PWM signal generator circuit 20 may be such that a minimum value of an ON time or OFF time is set in accordance with specifications). A switch SW 30 is driven by the switch drive signal Vdrv 22, as a result of which an output voltage Vout 44 in an output circuit 40 is maintained at a predetermined target value by a negative feedback control. The output circuit 40 is configured to include an inductor L 41, an output capacitor C 42, and a commutating diode D 43 that contribute to an accumulation and release of energy, wherein the output voltage Vout 44 resulting at one terminal of the output capacitor C 42 is supplied to a load (not shown).
Normally, as the DC-DC converter control circuit is such that the response of the negative feedback control loop controlled by the error amplifier 10 is set to be somewhat slow in order to stably operate the DC-DC converter, time is needed until the output voltage Vout 44 is static at the target value when a load current (a current flowing from the inductor L 41 and output capacitor C 42 in which energy is accumulated to the load (not shown)) increases suddenly, and there is a problem in that the output voltage Vout 44 drops considerably.
In response to this, a method whereby it is detected that an output voltage Vout has dropped below a predetermined value, a switching frequency is temporarily switched to a high frequency with this as a trigger, and an inductor current is increased, is disclosed in JP-A-2010-022186.
With the method disclosed in JP-A-2010-022186 too, it is thought that a certain effect for not allowing a large drop in the output voltage Vout is obtained. However, as an ON time period at a point at which an output voltage fluctuation occurs varies depending on operating conditions, and also changes during a transient response, it is difficult to choose an optimum switching frequency for all conditions with the method disclosed in JP-A-2010-022186 (while the effect is insufficient when a switching cycle is too long in comparison with the ON time period, the ON condition continues when the switching cycle is shorter than the ON time period).